[en] Highlights: • The performance of perovskite solar cells is boosted with sub-nm interfacial layers. • The interfacial layers facilitate a fast electron sweep-out. • The devices exhibit exceptional power conversion efficiencies up to 18.8%. • The efficiencies increase 25% compared to the one without the interfacial layer. In this paper, we demonstrate that the performance of perovskite solar cells can be largely boosted with sub-nm pyridine-containing small-molecule electron interfacial layers. These vacuum-deposited sub-nm layers between perovskites and electron transport layers create a permanent dipole moment that improves the interfacial energy level alignment and facilitates a fast electron sweep-out. With these interfacial layers, the devices exhibit exceptional power conversion efficiencies up to 18.8%, a 25% increase compared to that of the one without the interfacial layer.